Aldous Snow is a world-famous rock star well past his prime. Following a conversion to sobriety, the one-time junkie stopped making trashy odes to dirty deeds and got a social conscience. His last record, African Child, was, well, about the plight of African children, like Paul Simon's Graceland as recorded by Mötley Crüe. It tanked, Snow's relationship to pop diva Jackie Q fell apart, and he went off the wagon. Three years later, though, and Snow's live album recorded a decade prior at L.A.'s Greek Theatre continues to shift units and a junior record exec looking to impress his boss pitches the idea of an anniversary comeback. "Fine," says the boss, "as long as you personally make sure he shows up."

This is the basic pitch of Get Him to the Greek, a pseudo-sequel to the hit comedy Forgetting Sarah Marshall. In Greek, Russell Brand reprises the role that brought him to the attention of the movie-going public, and Jonah Hill returns as a new character though one remarkably similar to the uber-fan he played in Sarah Marshall. He's the junior record exec, Aaron Green, and his boss is Sergio Roma (Sean "P. Diddy" Combs), an alpha male who reminds rappers to be gangsta and conducts his business meetings while holding a letter opener that looks like a dagger. Aaron is dispatched to London a mere 72 hours before the big show. There's a lot of trouble a perpetually wasted rock star can get up to in three days, and Aaron is going to find out exactly how much.

Get Him to the Greek is helmed by Nicholas Stoller, who cut his directorial teeth on Sarah Marshall. He wrote the screenplay this time around and in doing so has managed to make a sequel every bit as funny as its original source. Russell Brand is an unstoppable screen presence, and he propels this movie from start to finish with impish glee and manic mood swings. The comedian has clearly dreamed of being a rocker his whole life, and he's studied Mick Jagger's moves, Marc Bolan's fashon, and Bob Dylan's cruel, manipulative streak. Watch the scene in Las Vegas where Brand dresses down Jonah Hill for losing his drugs, and compare it to Dylan getting upset about the broken glass in Don't Look Back. It's uncanny.

For his part, Jonah Hill plays a variation on his usual shy and awkward routine, but with an underlying sweetness that makes him a perfect foil for Brand. Everything you need to know about their relationship comes when the pair burst out of a Las Vegas hotel to the strains of T. Rex's "20th Century Boy." Aaron is looking over his shoulder, terrified at what is chasing them, while Aldous is laughing and having the time of his life. Gone are the foul-mouthed rants Hill delivered in Superbad and Knocked-Up, instead he serves as the straight man in over his head, vomiting on his clothes, and trying to hold everything together, including his own crumbling relationship. His girlfriend is played by Mad Men's Elizabeth Moss, who gets to be the center of one of the most uncomfortably funny scenes in the movie when Aldous and Aaron get back to L.A. In that sequence, Aldous turns the tables by offering relationship advice to Aaron, whose suggestions that the rocker reunite with his father (Colm Meany) and Jackie Q (Rose Byrne) all turned out bad. It's a sinister move, but it opens the way to the movie's emotional resolution.

Like the best Judd Apatow-produced comedies, Get Him to the Greek has some real feelings underneath the laughs, and Stoller manages to work in actual character growth without making it feel forced or overly sentimental. It's a pretty impressive turn, since everything prior to that in Get Him to the Greek is as far from sentimentality as you can get. Aldous leads Aaron across the U.S. on the most drugged-out, sexed-up road trip since Raoul Duke and Dr. Gonzo burned rubber for Sin City. It's the funnest party you're glad you never attended, and in addition to the credibly humorous Aldous Snow originals, Stoller DJs the soiree with rockin' tunes by the Stones, New York Dolls, the Ramones, and others. Thank God, a movie about music that gets the music right!

Stoller also peppers Get Him to the Greek with a good amount of real cameos. Christina Aguilera, Pink, Pharrell Williams, and Metallica drummer Lars Ulrich all make appearances as themselves, as do a litany of bottom-feeding entertainment reporters. The most impressive of the on-screen musicians, however, is P. Diddy. The rapper/producer practically steals the movie the way Brand stole Sarah Marshall. His is the most forceful performance, and he turns every scene upside down. (Also, stay until the end of the closing credits; Diddy gets one last laugh.) Makes you wonder if Stoller has a third movie in him, this time spotlighting Sergio Roma.

Last year, the hit summer comedy was The Hangover, a tale of men behaving badly. I guess there really is something about bad boys, because I could easily see Get Him to the Greek getting similar traction. I actually think Greek might be the better movie; funnier, at the least, and easily more comfortable with its emotional side. You couldn't ask for a more consistent movie in terms of delivering the laughs. In music terms, it's all singles and no album cuts--just one killer hit after another.